Interpretive Summary: Slowing the rate of apple fruit ripening during storage allows for more orderly marketing of high quality fruit over a longer storage period. New methods to reduce the rate of ripening are needed, particularly those that take advantage of the capacity to manipulate the natural processes of ripening without the use of synthetic chemicals. The present study evaluated how compounds naturally present in apples, nitric oxide and nitrite, act to modulate ethylene production in apple fruit tissues. The results indicated both compounds can reduce production of ethylene, the natural promoter of apple fruit ripening.

Technical Abstract:
‘Golden Delicious’ apple [Malus sylvestris var. domestica (Borkh.)] cortex disks suspended in solutions containing a nitric oxide ('NO) donor [S-nitrosoglutathione (GSNO) or sodium nitroprusside (SNP)], 'NO gas, or nitrite (KNO2) were utilized to identify impacts of 'NO on ethylene production and NO2- on 'NO and ethylene production. Treatment with GSNO or SNP reduced ethylene biosynthesis compared to control treatments containing equimolar concentrations of oxidized glutathione (GSSG) or Na4(CN)6, respectively. Apple disk exposure to 'NO gas did not impact ethylene production. Treatment with NO2- resulted in increased 'NO production and decreased ethylene biosynthesis. Generation of 'NO increased linearly while ethylene generation decreased exponentially with increasing NO2- treatment concentration. 'NO was enhanced in autoclaved tissue disks treated with NO2- suggesting that its production is produced at least in part by non-enzymatic means. While this evidence shows 'NO is readily generated in apple fruit disks by NO2- treatment and ethylene synthesis is reduced by 'NO / NO2- generated in solution, the exact nature of 'NO generation from NO2- and ethylene synthesis modulation in apple fruit disks remains to be elucidated.